Gold has been widely used as a plating material, electric and electronic materials, a medical material and the like, besides jewelry. As gold is expensive, it has been desired to collect gold from various kinds of wastage or waste fluid. However, the quantity of gold contained in the wastage is small, and it is difficult to selectively separate and collect gold from other metals which exist in large amounts.
In a conventional method of collecting gold from various kinds-of solid wastage, the solid is dissolved in aqua regia, and gold is collected from the solution by a metal substitution technique or the like. However, since the regulation on nitrogen in drainage has been recently tightened, the collection using the aqua regia is getting difficult to implement.
The following methods have been also proposed as methods of separating and collecting precious metals:
(a) Solvent Extraction Method and Ion Exchange Method
A solvent extraction method and an ion exchange method have been recently adopted as methods for collecting precious metals from an anode slime which is generated in an electrolytic smelting of copper, nickel and the like. In such a collecting process, after metals are completely dissolved in hydrochloric acid containing chlorine gas, the metals are individually collected by the solvent extraction method or the ionic exchange method.
With regard to the collection of gold, a solvent extraction method using dibutyl carbitol is adopted in many countries including Japan. Such a solvent extraction method is, for example, described in detail in non-patent document 1 listed below.
(b) Method Using Chemically-Modified Cellulose
Chemical modification of cellulose has been widely researched, and many adsorbents have been put into practice for analytical chemistry and medical use. For example, non-patent document 2 listed below describes cellulose in detail.
For example, the cellulose in which various functional groups, such as a diethylaminoethyl (DEAE) group, is introduced by chemical modification is used for separation and refinement of biogenic substances, such as an enzyme, a plasma component, and other functionality protein materials.
Moreover, there are some researches regarding collection of precious metals contained in various waste fluids and wastage using adsorbents prepared by chemical modification of a cellulose-base material such as paper. For example, non-patent document 3 listed below reports an adsorbent in which a primary amino group is fixed by the chemical modification of wastepaper.
<Non-Patent Document 1>
B. F. Rimmer, “Refining of gold from precious metal concentrates by liquid-liquid extraction”, Chemistry & Industry, Jan. 19, 1974, No. 2, pp. 63-66
<Non-Patent Document 2>
“Dictionary of cellulose”, pp. 131-165, “4.2 Chemical reaction of cellulose and derivative”, and pp. 539-545, “7.5.4 Ion exchange material”, Cellulose Society of Japan
<Non-Patent Document 3>
KAWAKITA Hidetaka, INOUE Katsutoshi, OHTO Keisuke, ITAYAMA Kyoko, PARAJULI Durga, “Preparation of Amine-Type Adsorbent Using Wastepaper and Adsorption of Metal Ions”, Waste Management Research 17(3), May 31, 2006, pp. 243-249